type Length<T extends readonly any[]> = T['length']


//tuple 与 array 的区别

const b = ['1','2','3'] as const

//元组
type bTuple = typeof b

//数组
const a = ['1','2','3']
type aTuple = typeof a


//1. tuple 的长度和类型都是确定的 可以理解为是一个写死了的数组 的类型